Due to unusually good mechanical properties, such as toughness, pliability, elasticity, and mechanical strength, polyamides belong to a class of high performance polymers with significant technical importance.
Polyamides are polar polymers with a high melting point of generally above 250° C. Only high performance pigments with outstanding heat stability can be used for coloring polyamides in a melt process. Since few organic pigments possess the properties needed to color polyamide, the availability of shades is limited. For this reason, large quantities of polyamide fibers are still bath dyed using special dyes like for example the acid dyes.
Many patents describe the dyeing of polyamide materials with dyes, in particular with acid dyes. For example U.S. Pat. No. 3,619,123 describes a process for dyeing synthetic polyamide fibers in the presence of one or more aromatic sulfonic acids to produce uniform dyed fibers. U.S. Pat. No. 4,438,140 describes salts of acid colorants and specified copolymers containing tertiary amino groups for its use in cosmetics. U.S. Pat. No. 6,136,433 describes melt-spinning a nylon fiber from a host polymer formed from a mixture of amide monomers and at least one hindered piperidine compound. A colorant is dispersed throughout the host polymer.
U.S. Pat. No. 4,374,641 describes a polymeric color concentrate for thermoplastic polymeric materials and solution dyeing of a nylon fiber. The color concentrate is prepared from a blend of a water or organic solvent-dispersible polymer and a soluble dye or pigment. The preferred polymer is a polyamide blend with a polyamide component having improved basic dye affinity, as described in U.S. Pat. No. 3,846,507.
Japanese Patent No. 60/162,881 describes shaped goods comprising of a polyamide and melamine derivative by immersing the shaped goods in an aqueous solution containing 0.1 to 1.5 wt. % of acetic or formic acid or ammonium sulfate at 40 to 45° C. and adding 0.1 to 1.0 wt. % of an acid dyestuff, elevating the temperature of the dyeing solution to 80 to 100° C. in 30 to 60 minutes and maintaining that temperature for 30 to 60 minutes then washing and drying the goods.
Japanese Patent No. 09-067781 describes black metal complex dyes and compounds having an absorption maximum at 650-800 nm for dying leather and fibers.
Polish Patent Nos. PL 147,938, PL 153,173 and PL 153,174 describe the manufacture of black 1:2 chromium-azo compound complexes for dyeing wool, polyamide fibers and leather, and U.S. Pat. No. 4,553,976 describes 1:2 chromium or cobalt complexes of azo dyes for dyeing natural or synthetic polyamide fibers.
U.S. Pat. Nos. 4,328,159 and 4,309,180 describe anthraquinone acid and/or fiber reactive dyes for dyeing wool and polyamide fibers or leather.
German Patent Nos. 4,408,526 and 19,518,849 and U.S. Pat. Nos. 6,033,445 and 4,309,180 describe anthraquinone compounds for dying synthetic polyamide(s), wool, leather and as printing inks.
Commercially available dyes that are used to dye polyamide articles in a bath dyeing process, are commonly formulated. That is, they contain additives and salts to increase the speed and color yield of the dyeing process. The dye concentration of such formulations is only about 40 to 80%. The resulting dyed polyamide articles, in particular the fibers need to be washed with plenty of water.
Due to the incompatibility of such additives found in dye formulations, commercially available dyes cannot be used directly in a melt spinning process to color polyamide fibers. Additionally, such formulations frequently manifest insufficient heat and light stability when applied by the melt spinning process.
None of the above literature describes the use of the claimed dyes for coloring polyamide in an extrusion, molding or melt spinning process. Surprisingly, it was found that selected dyes when used in their unformulated form can be advantageously employed for coloring polyamide articles, such as flocks, granules, wires, ribbons, foils, sheets, molded parts or fibers, in particular textile fibers like nylon-6 fibers in a melt process.
Thus, the present invention relates to a process for the preparation of colored polymeric articles having high processing temperatures, such as greater than 220° C., preferably greater than 240° C. and molded articles made therefrom by employing specific heat stable unformulated dyes in the melt process, for example the melt spinning process. Processing temperatures are the temperature ranges commonly provided by the polymer suppliers and generally do not exceed 340° C., more preferably 320° C. Thus, the selected dyes allow for the coloring of for example polyamide fibers in various shades very economically using the melt spinning process instead of bath dyeing.